Electronic article surveillance (EAS) systems have, in recent years, become increasingly commonplace. Such systems are now installed in a majority of academic and public libraries and are so common in retail stores as to not even cause a second look.
One type of EAS system in which alternating magnetic fields are employed typically utilizes panels or lattices on both sides of an exit way, thereby defining an interrogation zone through which protected articles bearing the EAS markers must pass. Both drive coils and sense coils are generally located within each lattice. For example, U.S. Pat. No. 4,994,939 (Rubertus) discloses a previously-preferred lattice assembly for housing both types of coils side by side, and in which a nulling mechanism is provided, thereby minimizing inductive coupling between the respective coils. As the null condition is affected by both ferrous objects near the lattice and by ambient electric currents, that mechanism enables the null condition to be adjusted during installation. While that patent facilitates certain improvements in the ease of construction, ease of installation, and usefulness with various types of systems and coil configurations, it has not proven to be fully satisfactory.